WIRELESS INFRARED COMMUNICATIONS
Download Free Wireless Infrared Communications.pdf Wireless infrared communications refers to the use of free-space propagation of light waves in the near infrared band as a transmission medium for communication(1-3), as shown in Figure 1. The com- munication can be between one portable communi- cation device and another or between a portable de- vice and a tethered device, called an access point or base station. Typical portable devices include laptop computers, personal digital assistants, and portable telephones, while the base stations are usu-ally connected to a computer with other networked connections. Although infrared light is usually used, other regions of the optical spectrum can be used (so the term \wireless optical communications” instead of \wireless infrared communications” is sometimes used).
Another important way to characterize a wireless infrared communication system is by the \link type”, which means the typical or required arrangement of receiver and transmitter. Figure 2 depicts the two most common con¯gurations: the point-to-point sys-tem and the di®use system. The simplest link type is the point-to-point sys-tem. There, the transmitter and receiver must be pointed at each other to establish a link. The line-of-sight (LOS) path from the transmitter to the receiver must be clear of obstructions, and most of the trans-mitted light is directed toward the receiver. Hence, point-to-point systems are also called directed LOS systems. The links can be temporarily created for a data exchange session between two users, or estab-lished more permanently by aiming a mobile unit at a base station unit in the LAN replacement applica-tion.
In di®use systems, the link is always maintained between any transmitter and any receiver in the same vicinity by re°ecting or \bouncing” the transmitted information-bearing light o® re°ecting surfaces such as ceilings, walls, and furniture. Here, the trans-mitter and receiver are non-directed; the transmitter employs a wide transmit beam and the receiver has a wide ¯eld-of-view. Also, the LOS path is not re-quired. Hence, di®use systems are also called non-directed non-LOS systems. These systems are well suited to the wireless LAN application, freeing the user from knowing and aligning with the locations of the other communicating devices.
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